The present invention relates to a belt retractor provided with a force limiter, whereby the belt retractor has as a force limiting device at least one energy absorbing element that is linked to the spool and via a profiled head to the blocking apparatus of the belt retractor and a switching device is provided that adjusts the energy absorption and that is switchable via an independent drive. Such belt retractors can be designed both as self-blocking belt retractors with a vehicle-sensitive and/or belt-sensitive controllable blocking apparatus and as so-called limit fitting in accordance with EP 0 773 147 A2.
WO 97/49583, which forms the generic type, describes a self-blocking belt retractor with the features specified in the foregoing; in the exemplary embodiments individually detailed therein provided as energy absorbing element is a torsion bar with two or three sections switched one after the other, and also described is the arrangement of two energy absorbing elements switched parallel to one another. The associated switching device can only be switched under a load that is, can only be switched given the application of great actuating forces when energy absorption has already been turned on, because an existing force- or load-transferring coupling between the spool and torsion bar has to be overcome, i.e., there must be a switch to such a coupling. The design and operative complexity required for this is correspondingly high. The object of the invention is therefore to provide in a belt retractor having the generic features a reliable switching device that works independently of a force transfer already existing between spool and torsion bar.
This object is achieved including advantageous embodiments and further developments of the invention from the contents of the patent claims that follow this specification.
The basic idea of the invention is that the switching device, which can be switched at any time via the drive arranged independent from the spool and/or switching device has a pawl borne with a tendency to open that is held in its coupling position by means of a to spool ring that is displaceable in the direction of the spool axis, and in that the spool ring can be axially transferred by means of a pyrotechnically drivable adjusting apparatus into a position in which the spool ring makes it possible to reverse the pawl from its coupling position to its release position. Since the at least one pawl for connecting the torque tube and the spool is borne with a tendency to open, no more actuating forces occur for moving the pawl once the pawl has been released by the displacement of the spool ring.
In accordance with one exemplary embodiment of the invention, it is provided that at least two energy absorbing elements are provided arranged in series or parallel to one another, and that the switching device switches from one energy absorbing element to the other energy absorbing element when the drive is triggered.
In accordance with another exemplary embodiment of the invention, it is provided that the torsion bar has at least two sections with different cross-sections arranged in series to one another for a establishing a different energy absorption, and a torque tube is provided that connects at least one section of the torsion bar and the spool in a form-fit, as such a design of a belt retractor is known in principle from WO 97/49583.
In an alternative embodiment of two energy absorbing elements, it can be provided that a torsion sleeve is arranged connected in switched parallel to the torsion bar, and torsion sleeve or torsion bar can be switched off by means of the switching device allocated to the torsion sleeve and that allocated to the torsion bar.
In accordance with one exemplary embodiment of the invention, it can be provided that the spool ring is connected to the spool via form-fit designs and rotates together with it.
In particular, it can be provided that the pawl is pivotably borne in a recess in the cross-section of the spool, and the spool ring is arranged spanning the exterior circumference of the spool such that the spool ring in its position maintaining the pawl in its coupling position covers the recess.
For effecting the change in position of the spool ring, it can be provided that the control apparatus comprises a set collar that is arranged on the belt retractor rotatable under the effect of a drive across a limited area of rotation for displacing the spool ring and that is supported against a cover of the belt retractor by at least one ramp inclined in the axial direction of the spool and that can be displaced axially due to its twisting, whereby in accordance with one exemplary embodiment of the invention a plurality of ramps are distributed across the circumference of the set collar and the cover. Such a control apparatus is associated with the advantage of an additional servo-effect, since due to the helical movement produced in this manner only a small radial force must be applied in order to produce a much greater axial force for displacing the spool ring and therefore for producing the switch movement under a load.
With regard to the design of the drive for rotating the set collar, a linearly displaceable pyrotechnically driven piston can be provided that tangentially impacts a shoulder projecting radially from the set collar. This stationary external arrangement of the pyrotechnic drive substantially simplifies the electrical control, since it is not necessary to transfer electrical signals to the rotating spool and the pyrotechnics attached thereto.
The inventive coupling between torque tube and spool makes it possible in accordance with one exemplary embodiment of the invention to arrange a deformable element between spool and torque tube. In accordance with exemplary embodiments of the invention, the deformable element can be designed as shearing bars extending in the circumferential direction of spool and torque tube or as bending bars arranged radially between spool and torque tube. In an additional embodiment of the invention it can be provided that the deformable element is designed as bending bars arranged radially between spool and torque tube. This ensures a gentle transition from the first force level to the other force level.
With respect to the cooperation between the belt force limitation created in the belt retractor and the airbag located in the vehicle, the point in time at which the switch takes place from the higher force level to the lower force level is very important. For a control in this regard, in accordance with one exemplary embodiment of the invention it is provided that for igniting the drive for the control device a time switch is provided that is activated by the vehicle sensor and that involves a pre-selected period of time. In this exemplary embodiment of the invention, the ignition occurs at a pre-specified point in time independent of other accident conditions.
In an alternative embodiment of the invention it is provided that a device is provided for determining the revolutions of the spool under a load after a pre-selected threshold has been exceeded for determining the belt withdrawal effected by the force limitation, and the ignition of the drive for the set collar occurs when a pre-selected belt withdrawal has been achieved. In this embodiment of the invention, the belt withdrawal occurring during the accident and caused by the effect of the force limiting device of the belt retractor is used as a measure for switching the level of the force limiting device.